Evaluating on the spatial localization cues of binaural sound pressure recorded via behind-the-ear microphones in a hearing aid

Spatial hearing ability enables people with normal hearing to localize a sound source and utilizes the cocktail party effect to detect the target speech information in a noise environment. Hearing-impairment causes not only hearing loss but also the degradation of spatial auditory ability. Hearing aid is desired to improve the spatial auditory ability of some hearing-impaired people, in addition to compensating hearing loss. However, the microphones for conventional behind-the-ear (BTE) hearing aid are located behind the pinnae rather than in the entrances of ear canal, which may cause distortion in spatial cues in the recorded binaural signals. The present work comprehensively evaluates the spatial hearing cues recorded by BTE-microphones. The head-related transfer functions (HRTF) for a KEMAR artificial head and eight human subjects, at three BTE positions and the entrances of blocked ear-canal, are measured respectively. Analysis from the HRTF data indicates that BTE microphone recording basically reserves the interaural time difference and interaural level difference as lateral-direction information. It also reserves the dynamic cues, but obvious distortions appear in the spectral cues at high frequencies. However, due to the redundancy among different spatial information, it can be inferred that dynamic cues alone may provide appropriate front-back and vertical-direction information.